Role of the Initial Degree of Ionization of Polyethylenimine in the Dispersion of Silicon Carbide Nanoparticles

The role of the initial degree of ionization (α i ) of polyethylenimine (PEI) in the dispersion of SiC nanopartilces in water was investigated by sedimentation and rheological measurements. The ionization of PEI was characterized by potentiometric titration, which indicated a pH‐dependent conformational transition. The dispersion of SiC particles in the presence of PEI was found to strongly depend on the α i . In the presence of 0.4% by weight PEI, the 23.8% SiC by volume (Φ SiC = 23.8) slurries showed a Newtonian behavior for α i = 0.12–0.4 values, whereas a shear‐thinning behavior was observed for α i > 0.4 in the optimal pH range of around pH 4. The rheological behavior of the slurries exhibited a strong dependence on the concentration of PEI of α i = 0.12–0.4 and the slurry showed a Newtonian behavior at an optimal concentration of 0.4% by weight. The stabilization may be dominated by an electrosteric effect arising from the adsorbed PEI of α i = 0.12–0.4. The flocculation mechanism of the slurries with PEI of α i > 0.4 is also discussed.